Gayle and Sheila Muhs gave trespassers a blunt warning. They posted a large sign outside their Texas home saying trespassers would be shot and survivors would be shot again.

They weren't joking.

The Muhs are currently being held on charges of aggravated assault for allegedly firing at least two shotgun blasts at a pair of packed cars that stopped outside their rural Texas house. Those charges are expected to be upgraded to murder, since a 7-year-old boy who was wounded in the assault has died from shotgun pellets to his head and face.

But police said the families in the two cars were driving on a public road when the Muhs opened fire from their house, killing Donald Coffey Jr. and hitting three others, including the boy's 5-year-old sister.

Outside the Muhs' house is a handpainted sign complete with misspelling and exclamation points that warns: "Trespassers Will Be Shot. Survivers Will Be Reshot!! Smile I Will."

Police got a 911 call just after 9 p.m. Thursday, DeFoor said, from Sheila Muhs who "reported there were people in jacked up four-wheel automobiles ... and that she shot them." She also reported that the vehicles were destroying the nearby levees.

But in reality, DeFoor said, the families in the two cars had done nothing illegal. And, he said, they never set foot on the Muhs' property.

DeFoor said the Coffey family -- mom Becky, dad Donald Sr. and their three children -- were visiting friends along with Patrick Cammack and Cindy Nelton in the Muhs' neighborhood near Dayton, Texas, about 45 miles east of Houston.

The two families had planned to go off-roading at the nearby government-owned levees on the way home, an activity that is both popular and legal in the area, DeFoor said.

In the Jeep were Cammack, 30, Donald Coffey, 30 and Donald Jr., 7. In the following Ford SUV were Becky Coffey, Nelton and the Coffey's 5-year-old daughter, Destiny, and 11-year-old son.

The two cars stopped on the county-owned road outside the Muhs' home so one of the boys could go to the bathroom by the side of the road.

That's when, DeFoor said, the couple ran out of their house.

"Sheila Muhs started cursing at them 'Get off our property,'" DeFoor said and fired off at least one round, causing the Jeep, which had started to leave, to veer off the road.

Muhs, he said, then put the shotgun down and chased after the Jeep on her all-terrain vehicle, eventually catching up to it on the levee about 100 yards away, the ATVs headlights pointed at the Jeep.

While that was happening, DeFoor said Gayle Muhs picked up the discarded shotgun and fired at the SUV. DeFoor said the trajectory of that shot showed that the back of the SUV was sprayed with pellets, it's rear window blown out.

"The SUV was in the process to flee," the officer said.

Nelton told the Houston Chronicle that they yelled at the Muhs after the first shot that they had kids in the car and to stop shooting, but another gunshot -- possibly more -- is all they heard in return.

Nelton said Destiny was in the back of the SUV screaming.

"She said, 'Mama, they shot me. Mommy, they shot me.' There was blood all over her," Nelton told the Houston Chronicle.

When it was over, Destiny had been shot in the elbow, Donald Coffey Sr. in the shoulder and Cammack, who was driving the Jeep, in the base of his skull. Little Donald Coffey, however, had been hit by several shotgun pellets in the face and head.

'They Need to Be Dead'

DeFoor said the two families gathered up their wounded into the SUV and raced to the nearest fire station about a mile away where medical helicopters and ambulances transported everyone to the hospital.

DeFoor said the investigation is ongoing, but police believe the Muhs may have fired as many as four shots from the 12-guage pump shotgun, each one spraying 15 pellets.

He called it "a total disregard for whoever may be out there."

Nelton declined to speak to ABCNews.com about the shooting, saying she's trying to take care of Cammack.

"We're all dealing with this very, very hard," she said.

She told the Houston Chronicle that she only had one wish for the Muhs. "They need to be dead," Nelton told the newspaper.

Gayle Muhs is being held on $25,000 bond for one count of assault, and Sheila Muhs, who faces two counts of aggravated assault, is being held on a $525,000 bond. DeFoor said the Sheriff's Office would be submitting further information to the district attorney's office today and expects the charges to be upgraded to murder.

Stephen Taylor, the court-appointed attorney for Sheila Muhs said he had not yet spoken to his client but probably would do so tonight.

"I don't know anything more than what I've read in the newspapers," he said.

The court said Gayle Muhs did not yet have a lawyer.

Though Donald Coffey Jr. was pronounced dead, DeFoor said his family had kept the boy on life support while doctors prepared to transplant his organs.

Cammack, he said, had been released from the hospital, the pellet still lodged at the base of his skull. Destiny and Donald Coffey Sr. were also treated for their wounds, he said.

DeFoor said the Muhs were known to police and have previous arrests though neither he nor the court could say what the charges were or when.

Most of the people in the area own firearms, he said, saying that that specific neighborhood was at "lower socio-economic level."

Texas does have a "castle" law that allows property owners to shoot if someone is trespassing on their property at night. But that law, he said, does not apply in this case.

While guns may have been used to settle disputes in the 1800s, he said, Texas is "not the Wild West."